1. Field of the Invention
The present invention relates to the power control of a fax/modem, and more particularly to an automatic power control apparatus of a PC mounted fax/modem.
2. Discussion of the Related Art
A conventional PC mounted fax/modem apparatus as shown in FIG. 1 includes a ring signal sensing section 100 for searching out a signal received from a telephone line and for changing a logic value in a flag register to a logic value of one from a logic value of zero when a telephone ring signal is produced. This indicates that a fax has been received or that data has been received over a modem. An MCU 101 controls a hook switch section 102 as the logic value of one is stored in the flag register of ring signal sensing section 100. Simultaneously, the MCU 101 decodes the data received via the telephone line to provide corresponding fax or modem data. Hook switch section 102 connects or cuts off the hook switch in accordance with a control signal from MCU section 101 for connecting or cutting off the telephone line. A PC power source section 103 is supplied with AC power via a power converter for converting it into DC power. The PC power source section 103 supplies power for driving the various blocks of FIG. 1.
The operation of the automatic power control apparatus of the conventional PC mounted fax/modem will be described below.
With the power switch of the PC turned on, ring signal sensing section 100 receives the external ring signal via the telephone line. Ring signal sensing section 100 monitors the rising edge of a pulse generated when the telephone bell is to be rung, i.e., when the ring signal is received. Upon receiving a ring signal, ring signal sensing section 100 instantly writes a logic value of one into the 1-bit flag register internally mounted therein. The flag register in ring signal sensing section 100 stores a logic value of zero when the PC is operated as a transmitting fax/modem. When the PC is operated in the fax/modem mode, the telephone bell cannot be rung. The logic value changes from zero to one at the moment the telephone call is externally made.
The MCU 101 for controlling respective blocks searches out the flag register of ring signal sensing section 100 to read out the stored value. The MCU 101 supplies the read-out value as the control signal to hook switch section 102 to connect the hook switch if the value is one to permit the externally transmitted data to be received. The MCU 101 determines whether the externally received data is fax data or is general PC communication data, and accordingly identifies it as fax data or PC data. The MCU 101 determines the completion of the receipt of data by determining that no data is received for one frame period and will then open a contact point of hook switch section 102. This generates a control signal to cut off the telephone line. In other words, the hook switch section 102 turns the telephone line on and off in accordance with the control signal from the MCU 101.
However, since the conventional power control apparatus of a PC mounted fax/modem cannot perform the fax/modem function when the power of the PC is off, the PC must be maintained on in order to execute the fax/modem function, which in turn wastes too much power.